Function onChange

static/editor.md/lib/codemirror/addon/display/placeholder.js:47–53

(cm)

    if (isEmpty(cm)) setPlaceholder(cm);
  }
  function onChange(cm) {
    var wrapper = cm.getWrapperElement(), empty = isEmpty(cm);
    wrapper.className = wrapper.className.replace(" CodeMirror-empty", "") + (empty ? " CodeMirror-empty" : "");

    if (empty) setPlaceholder(cm);
    else clearPlaceholder(cm);
  }

  function isEmpty(cm) {
    return (cm.lineCount() === 1) && (cm.getLine(0) === "");